Skin effect heat tracing technology for pipelines

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Pipeline skin effect heat tracing technology in petrochemical enterprises

pipeline skin effect electric heat tracing (heating) technology is a new metal pipeline heating method emerging in recent years. It is a new technology and process for heating and insulation of heat transmission pipelines in large petrochemical enterprises, which is referred to as sect method abroad. This heating technology has the advantages of high efficiency, adapting to the heat tracing and heating of all long, medium and short-distance metal infusion pipelines, and having the advantages of safety and reliability. The experimental machine is an instrument and equipment, system or device that tests and detects the strength, stiffness, hardness, elasticity, plasticity, toughness, ductility and surface and internal defects of materials (metal materials, non-metallic materials), parts, components and structures, and is convenient for installation and maintenance, Therefore, it is widely used in the pipeline transportation of liquid substances with different properties

II. Device composition and basic principle

1. Device composition

pipeline skin effect heat tracing technology device, which is basically composed of transformer, heating power supply, infusion pipe, heat tracing pipe and heat tracing cable, insulation layer, protective shell and other parts. Heating power supply is divided into power frequency heating power supply and medium frequency heating power supply; The infusion pipe and heat tracing pipe are ordinary steel pipes with a diameter of mm, which are intermittently welded on the infusion pipe; The heat tracing cable is threaded in the heat tracing pipe, and the outside is the insulation layer and protective shell. As shown in the figure:

2. Basic principle

when the power frequency alternating current passes through the heat tracing pipe wall through the cable, under the skin effect and proximity effect, the current does not uniformly follow the pipe wall, but concentrates on the inner surface of the heat tracing pipe. Under the action of the resistance of the pipe wall, the current is heated through the current, and the temperature of the infusion pipe is increased through conduction, while the voltage and current on the outer surface of the heat tracing pipe are zero, forming an insulating structure by itself, So that the liquid can be safely and reliably transported in the pipeline

according to the calculation, the maximum heating capacity of a single heat tracing pipe is 150w/m, and according to the temperature of the infusion pipe, for the 500N model, it is generally required to adopt the tensile test mechanism of a single arm (single column), design the number of heat tracing pipes and operating voltage, and can be equipped with up to 6 heat tracing pipes. Reliable grounding is provided at the end and middle of the heat tracing pipeline to prevent static electricity or induced electricity, so as to ensure the safe transportation of the liquid in the storage. Skin effect heat tracing and pipeline cathodic protection can be carried out at the same time

III. technical features

1. Strong adaptability and wide application range

it is suitable for the heat tracing and heating of all long, medium and short-distance metal infusion pipelines, and is suitable for different laying methods of pipelines and any places, such as underground direct burial, underwater, ground overhead; It is suitable for fields, mines, factories and inflammable and explosive places

2. Safe and reliable, easy installation and maintenance

the heat tracing pipe adopts steel pipe, which has high strength, tight sealing and good protection. The heat tracing cable adopts high-temperature fluoroplastic cable. The heat tracing pipe forms an insulation structure due to skin effect, so that the external surface of the infusion pipe and the heat tracing pipe is not charged. The infusion pipe is safely grounded every kilometer or so, and the grounding resistance is not greater than 4 Ω, so as to ensure that the infusion pipe is always zero potential and achieve safety and reliability. Compared with other electric heat tracing methods, the skin effect heat tracing method is convenient for maintenance and inspection, and there is almost no maintenance workload during its normal operation. Once a fault occurs, the fault point can also be easily found. Just open the grounding and pull box at both ends of the fault point, pull out the damaged cable and replace it. When there is a problem with the electric heating band, the whole heating band should be removed and the insulation layer should be destroyed before it can be repaired. Mg cable has the same problem

3. Energy saving, high heating efficiency

power frequency skin effect heat tracing belongs to isothermal heating method, with high heating efficiency. For example, the power frequency skin effect heat tracing energy consumption of oil pipeline is 23lkg/km standard coal. The energy consumption of thermal cycle or steam tracing is 1813kg/km standard coal. Skin effect heat tracing is uniform heating without local overheating. With the extension of pipeline transmission distance, increase the heating voltage

4. Automatic control can be realized

control and protection screens can be installed in the instrument room (duty room). Conventional protections such as short circuit and overcurrent are installed inside, and the temperature can be adjusted accurately through the temperature sensor. Realize automatic control and unattended, so as to meet the requirements of modern development of enterprises

5. Prefabrication in advance can be realized

the infusion pipe and the heat tracing pipe are welded together, and the insulation layer and protective shell are added outside, which can be prefabricated and processed in the prefabrication plant, which is convenient for construction and easy to ensure the project quality

IV. application field

this unit has ideal working characteristics

according to the different physical properties of the liquid in the pipeline, the temperature required to be maintained in the pipeline is also different. The power frequency skin effect pipeline heat tracing technology is mainly applied to the heat tracing of the pipeline and the heating, melting or intermittent oil transmission pipeline of the liquid or solidified medium in the pipeline. The applicable scope of this technology is mainly used for the following infusion pipelines:

L. it is used for heat tracing of antifreeze pipelines. The gas transmission pipeline contains saturated steam, and the temperature is required to be maintained at not less than 6 ℃

2. It is used in the fluid that is solidified at room temperature and the temperature of the pipeline is not lower than 50 ℃ during transportation. This kind of fluid can only become liquid and be transported when it is heated to a certain temperature. Such as transporting chocolate, milk, etc

3. The pipeline is required to maintain a temperature of 50 ~ 100 ℃, which is solid at room temperature or has high viscosity, which is difficult to flow, but it is easy to flow substances after heating to a certain temperature. Skin effect heat tracing can be used to prevent pipeline cooling and pipeline shutdown and restart. Such as gathering and transportation of heavy oil, high pour point oil, fuel heavy oil, coal tar, wax, etc

4. It is required to maintain a high temperature. The infusion pipeline with a temperature higher than 100 ℃ but lower than 150 ℃, such as sulfur, can become liquid only when it is heated at L30 ~ 140 ℃, which is easy to transport

5. Pipelines requiring isothermal heat tracing, such as long pipeline distance, are faced with many challenges in reducing the weight and thickness of packaging materials during transportation, and the temperature is not easy to be too high for medium transportation

6. Intermittently transported high pour point media or viscous media, such as intermittent loading of wharf fuel oil, ships, pipelines without cleaning, can be directly restarted, etc

skin effect heat tracing can be used for the above types of pipeline transportation. It is concluded from practice that this technical scheme has achieved good transportation effects and remarkable economic benefits

v. comparison with other heat tracing methods

it can be seen from the table that the two methods of electric heating band and Mg cable are more suitable for local heat tracing and short-distance heat tracing, such as the heating of valves, valve parts, bypass, short joints and short pipelines in the station. For medium and long-distance pipeline heat tracing, due to the work of a single heat tracing cable

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